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    <title>JavaScript第二课</title>
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<body>
    <h1>数据类型和变量</h1>
    <h2>数据类型</h2>
    <h3>Number</h3>
    <h3>字符串</h3>
    <h3>布尔值</h3>
    <h3>比较运算符</h3>
    <h3>null和undefined</h3>
    <h3>数组</h3>
    <h3>对象</h3>
    <h2>变量</h2>
    <h2>strict模式</h2>


    <h1 id='hh'>

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